This invention relates to compositions comprising a polymercaptan which has at least two mercaptan (--SH) groups and a compound which has at least three ethylenically-unsaturated double bonds. It also relates to the polymerisation of such compositions by means of actinic radiation and/or heat-activated free-radical catalysts, and to the use of the polymerised products as surface coatings, in printing plates and printed circuits, as adhesives, and in reinforced composites.
In published British Patent Application No. 2 012 780 A (U.S. Pat. No. 4,220,513) are described compositions comprising
(i) a compound containing in the same molecule both at least one 1,2-epoxide group and at least two groups chosen from allyl, methallyl, and 1-propenyl groups, e.g., 2,2-bis(3-allyl-4-(glycidyloxy)phenyl)propane and bis(3-(1-propenyl)-4-(glycidyloxy)phenyl)methane, and
(ii) a compound containing at least two mercaptan groups attached to aliphatic carbon atoms per molecule, e.g., pentaerythritol tetrathioglycollate.
The compositions are caused to polymerise by the reaction of mercaptan groups with the allyl, methallyl or 1-propenyl groups under the influence of actinic radiation or free-radical catalysts.
Such compositions which further contain
(iii) a heat-curing crosslinking agent for polyepoxides are also described; the polymerised products, containing more than one epoxide groups per average molecule, could thus be subsequently crosslinked in situ.
Published British Patent Application No. 2 012 781 (U.S. Pat. No. 4,308,367) discloses similar compositions, in which component (i) contains at least one phenolic hydroxyl group instead of at least one epoxide group, e.g., 2,2-bis(3-allyl-4-hydroxyphenyl)propane and bis(3-(1-propenyl)-4-hydroxyphenyl)methane, component (iii) being correspondingly a heat-activated crosslinking agent for phenol-aldehyde novolac resins. The polymerised products, containing more than one phenolic hydroxyl group per average molecule, could likewise be subsequently crosslinked in situ by heating.
We have now found that certain compounds containing acrylate or methacrylate ester groups can be caused to polymerise very rapidly by exposure to radiation or to the action of free-radical catalysts in the presence of certain mercaptans to form products having valuable properties. The acrylate or methacrylate esters employed also contain allyl, methallyl, and/or 1-propenyl groups. It is believed, although the usefulness of this invention does not depend on the truth of this belief, that the allylic type double bonds react preferentially with the mercaptan groups, thus facilitating the polymer-forming processes taking place by means of the double bonds in the acrylic or methacrylic groups. Whatever the mechanisms of the reactions may be, it has been found that the compositions polymerise rapidly to form surface coatings and adhesive bonds characterised by good resistance to deleterious environments such as hot humid conditions.